1. Technical Field
This invention relates to a magnetic recording medium, more particularly, to a magnetic recording medium for use in magnetic read/write equipment such as magnetic disk equipment known as hard disk drives (HDD), and further particularly, to the structure of a magnetic recording medium of the perpendicular recording type having a high recording density.
2. Background Art
High-capacity storage devices, especially hard disk drives featuring a high data transfer rate, quick access, high reliability and low price have marked a significant advance toward higher capacity and higher density. An improvement in areal recording density is accomplished by miniaturizing recording magnetic domains formed in the magnetic recording layer. At present, the density has exceeded 5 gigabits per square inch, with development efforts being made with the target on 10 gigabits to 100 gigabits.
Used as the magnetic head for write and read operation is a combined magnetic head in which an inductive head as the write head is combined with a magnetoresistive head (MR head) as the read head, which are mounted on a slider. Since the output of the MR head is determined by a magnetic flux change per circumferential unit length, in principle, the output does not decline even when the track width is minimized. The use of the MR head thus suggests a possibility to realize narrow tracks. The same applies to a giant magnetoresistive head (GMR head) with which a higher recording density is expected.
However, if the track width is too narrow, the interference or crosstalk between magnetic signals from adjacent recording tracks increases so that the degradation of read signals becomes a problem.
The areal recording density can also be increased by reducing the recording bit length. If the recording bit length is too short, the interference or partial erasure between magnetic signals from adjacent bits increases so that the degradation of read signals becomes a problem.
JP-A 9-297918 discloses a magnetic recording medium in which a plurality of recording portions are provided in the form of rectangular regions having two side lengths equal to a track width and a minimum bit-determining length, the plurality of recording portions are separated by space areas, and information is stored in the recording portions. This medium is a so-called patterned medium. The patterned medium is effective for suppressing the degradation of read signals by crosstalk and partial erasure.
The patterned medium permits the recording density to be further increased by employing the perpendicular recording mode.
In addition to regions where ordinary information is recorded, the magnetic recording medium in the hard disk drive must have regions for recording servo information for tracking by the magnetic head. However, it was not discussed in the prior art how to record servo information in a patterned medium of the perpendicular recording type.
The inventors have reached the conclusion that in a patterned medium, like data recording, servo information may be recorded in minute recording portions (to be referred to as unit minute recording portions, hereinafter). In that event, however, there arises a problem that servo information can be inadvertently rewritten or erased when data are recorded or erased.
An object of the invention is to prevent inadvertent rewriting or erasure of servo information in a patterned medium based on the perpendicular recording mode.
This and other objects are attained by the present invention which is defined below as (1) to (6).
(1) A magnetic recording medium for use in magnetic write/read operation by the perpendicular recording mode, comprising recording tracks each having an array of unit minute recording portions of a magnetic material separated by non-recording portions of a nonmagnetic material, each unit minute recording portion having a surface area and a thickness, wherein
the recording tracks include data regions and servo regions, the unit minute recording portions in the data regions have substantially the same surface area as the unit minute recording portions in the servo regions, and
ARS/ARDxe2x89xa71.5 provided that the unit minute recording portion has an aspect ratio which is the thickness divided by the square root of the surface area thereof, the unit minute recording portion in the data region has an aspect ratio ARD, and the unit minute recording portion in the servo region has an aspect ratio ARS.
(2) The magnetic recording medium of (1) wherein ARS/ARDxe2x89xa610.
(3) The magnetic recording medium of (1) wherein ARDxe2x89xa64.
(4) The magnetic recording medium of (3) wherein ARDxe2x89xa71.
(5) The magnetic recording medium of (1) wherein the unit minute recording portions are constructed of any one of Co, Coxe2x80x94Cr, Coxe2x80x94Crxe2x80x94Ta, Coxe2x80x94Crxe2x80x94Pt, Coxe2x80x94Pt, Fexe2x80x94Co, Fexe2x80x94Coxe2x80x94Pt, and X-Y-Co wherein X is at least one of Dy, Gd and Tb and Y is at least one of La, Pr, Nd and Sm.
(6) The magnetic recording medium of (1) wherein each unit minute recording portion is a single magnetic domain.
According to the invention, the aspect ratio in the servo regions is set at least 1.5 times the aspect ratio in the data regions. With this setting, the unit minute recording portions in the servo regions have a sufficiently high coercivity as compared with those in the data regions. This prevents erasure of servo information even when a record erasing magnetic field to be applied to only the data region is inadvertently applied to the servo region, when the magnetic recording medium is re-formatted, or when the recorded data in the data region is erased by an external magnetic field other than the record erasing magnetic field.